U.S. patent number 4,425,115 [Application Number 05/898,569] was granted by the patent office on 1984-01-10 for ultrasonic resonant vibrator.
Invention is credited to David G. Wuchinich.
United States Patent |
4,425,115 |
Wuchinich |
January 10, 1984 |
Ultrasonic resonant vibrator
Abstract
An ultrasonic resonant vibrator has a connecting portion
connecting an ultrasonic vibration transducer to a tool which
thereby ultrasonically vibrates at one end for fragmenting
contacted tissue. The connecting portion is bifurcated by a slot,
and a mount for mounting the vibrator in the handpiece is
positioned toward the transducer from the slot. This structure is
shaped, dimensioned and made of materials having acoustic
properties such that there is only one node of ultrasonic
vibrational movement between and including the slot and the mount
and this node is spaced from the mount toward the slot to obtain
increased ultrasonic vibration at the tissue-contacting end of the
tool for better fragmenting a wider variety of tissues.
Inventors: |
Wuchinich; David G. (New York,
NY) |
Family
ID: |
25409647 |
Appl.
No.: |
05/898,569 |
Filed: |
April 21, 1978 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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861599 |
Dec 19, 1977 |
4223676 |
|
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672814 |
Apr 1, 1976 |
4063557 |
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Current U.S.
Class: |
604/22; 310/26;
606/169 |
Current CPC
Class: |
A61B
17/22004 (20130101); A61B 17/22012 (20130101); B06B
3/02 (20130101); A61F 9/00745 (20130101); A61B
2017/320084 (20130101); A61B 2217/005 (20130101); A61B
2217/007 (20130101); A61B 2017/320088 (20130101) |
Current International
Class: |
A61B
17/22 (20060101); B06B 3/02 (20060101); B06B
3/00 (20060101); A61B 17/32 (20060101); A61M
1/00 (20060101); A61M 001/00 () |
Field of
Search: |
;128/24A,276,33R
;32/DIG.4 ;310/26 ;604/22 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Cohen; Lee S.
Attorney, Agent or Firm: Vorys, Sater, Seymour &
Pease
Parent Case Text
BACKGROUND OF THE INVENTION
This application is a continuation-in-part of U.S. patent
application Ser. No. 861,599 filed Dec. 19, 1977, now U.S. Pat. No.
4,223,676, which is a continuation of U.S. patent application Ser.
No. 672,814 filed Apr. 1, 1976 and now U.S. Pat. No. 4,063,557.
Claims
I claim:
1. An ultrasonic resonant vibrator comprising:
an ultrasonic vibration transducer for external electrical
excitation to vibrate; at an ultrasonic frequency;
a tool having a free end for output ultrasonic vibration;
connecting means connecting the transducer to the tool for
ultrasonically vibrating the tool with the vibrations from the
transducer at the resonant frequency of the resonant vibrator, the
connecting means having a slot bifurcating the connecting means;
and
mounting means spaced from the slot toward the transducer for
supporting the resonant vibrator;
the combination of the transducer, connecting means, tool and
mounting means defining the resonant vibrator and having the first
node of the ultrasonic resonant vibrations from and including the
mounting means toward the slot positioned away from the mounting
means toward the slot,
wherein said first node is positioned at a point where the gain in
ultrasonic vibration at the end of the tool from positioning the
first node toward the slot most exceeds the loss of ultrasonic
vibration at the end of the tool from damping the vibration with
the support of the resonant vibrator at the mounting means.
2. An ultrasonic resonant vibrator comprising:
an ultrasonic vibration transducer for external electrical
excitation to vibrate at an ultrasonic frequency;
a tool having a free end for output ultrasonic vibration;
connecting means connecting the transducer to the tool for
ultrasonically vibrating the tool with the vibrations from the
transducer at the resonant frequency of the resonant vibrator, the
connecting means having a slot bifurcating the connecting means;
and
mounting means spaced from the slot toward the transducer for
supporting the resonant vibrator;
the combination of the transducer, connecting means, tool and
mounting means defining the resonant vibrator and having the first
node of the ultrasonic resonant vibrations from and including the
mounting means toward the slot, positioned away from the mounting
means toward the slot,
wherein said first node is on a line normal to the longitudinal
axis which intersects the longitudinal axis approximately at the
end of the slot farthest from the mounting means.
3. An ultrasonic resonant vibrator dimensioned for mounting in a
handpiece for fragmenting tissue contacted with an end thereof, the
resonant vibrator comprising:
an ultrasonic vibration transducer for electrical excitation from
the handpiece to vibrate at an ultrasonic frequency;
a tool having a free end defining the end of the resonant vibrator
for ultrasonic vibration longitudinally of the tool to fragment
contacted tissue;
a connecting member connecting the transducer to the other end of
the tool for ultrasonically vibrating the free end of the tool, the
connecting member having an elongated slot diametrically
bifurcating the connecting member with the longitudinal axis of the
slot coinciding with the longitudinal axis of the resonant
vibrator; and
mounting means spaced from the slot toward the transducer for
mounting the resonant vibrator in the handpiece;
the combination of the transducer, connecting member, tool and
mounting means defining the resonant vibrator with a longitudinal
axis of each aligned along the longitudinal axis of the resonant
vibrator, each being dimensioned along the longitudinal axis
relative to the wavelength of the resonant frequency therein such
that the resonant vibrator is an integral multiple of one half the
wavelength of the resonant frequency long, and has one but only one
node of the ultrasonic resonant motion between and including about
the slot and the mounting means which one node is spaced from the
mounting means toward the slot,
wherein the resonant vibrator is further shaped, dimensioned and
has acoustic properties such that it has a resonant frequency of
about 23 kHz and the one node is positioned about at the end of the
slot farthest from the mounting means.
Description
This invention is directed to an apparatus for ultrasonically
fragmenting and aspirating tissue in a surgical operation.
Ultrasonically vibrated surgical tools for removing various types
of body tissues are well known. For example, certain of these
instruments are commonly used in removing cataracts from the eye as
illustrated by the assignee's U.S. Pat. No. 3,589,363 issued June
29, 1971 to A. Banko and C. D. Kelman. Another, the ultrasonic
dental prophylaxis unit as illustrated by the assignee's U.S. Pat.
No. 3,076,904 is a widely accepted and successful instrument for
cleaning teeth. Other specialized ultrasonically driven surgical
instruments have been patented, though the extent of their actual
use by others is unknown.
The assignee, however, has several prior patents and patent
applications which describe the use of ultrasonically vibrated
tools to remove tissues. Among these are U.S. Pat. No. 4,016,882
issued Apr. 12, 1977, U.S. Pat. No. 3,526,219 issued Sept. 1, 1970,
and U.S. Pat. No. 3,565,062 issued Feb. 23, 1971. None of the
instruments shown in these patents, however, has been entirely
satisfactory for removing all of the wide range of body tissues
which have markedly different mechanical characteristics; i.e.,
compliance, ranging from liquid to a relatively hard and brittle
material such as bone. Some tissues are therefore much more
difficult to fragment than others and instruments built according
to the patents have had difficulty providing sufficient ultrasonic
vibration, and particularly sufficient stroke, to fragment
effectively a wide enough variety of the tissues for its surgical
use.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a novel
surgical apparatus employing an effective ultrasonically vibrating
tool.
Another object of the present invention is to provide an
ultrasonically vibrating tool having aspiration means which are
isolated from a connecting member's mounting fixtures.
Yet another object of the present invention is to provide
ultrasonic surgical apparatus for fragmenting, and aspirating
highly compliant tissue containing blood.
It is therefore also an object of this invention to provide
apparatus for surgically removing tissue.
It is another object of this invention to provide apparatus for
surgically disintegrating and aspirating tissue in an effective
manner.
It is still another object of the present invention to provide
surgical apparatus having an ultrasonically vibrating tool with a
stroke of at least 5 mils (0.005 inch).
Still another object of this invention is to provide a high stroke
ultrasonically vibrating surgical handpiece.
Another object of the present invention is to provide a
conveniently held high power ulrasonic surgical tool having
aspiration and irrigation.
Other objects and advantages of the present invention will be
apparent to those skilled in the art from the description of the
drawings and preferred embodiment.
To these ends, a novel surgical apparatus for fragmenting, and
preferably aspirating, tissue is disclosed. The apparatus comprises
an ultrasonic resonant vibrator dimensioned to be mounted in a
handpiece and having an ultrasonic vibration transducer which is
electrically excited from the handpiece for ultrasonic vibration
and a tool having an end for fragmenting contacted tissue with
ultrasonic vibration thereof. A connecting structure, which may be
part of the tool but preferably is distinct therefrom to provide
amplification of the ultrasonic vibration as later described in
relation to a preferred embodiment, connects the tool to the
transducer for vibrating the tool. It has a slot bifurcating the
slotted portion of the connecting structure. A mounting arrangement
for mounting the resonant vibrator in the handpiece is positioned
along the resonant vibrator toward the transducer from the slot.
This resonant vibrator structure is shaped, dimensioned and made of
materials with acoustic properties in accordance with known design
principles such that in the resulting unique structure there is one
but only one node of ultrasonic vibratory motion between and
including the slot and the mounting means which one node is spaced
from the mounting means toward the slot.
It is well known in the design of ultrasonic resonant vibrators
that the mount for supporting the vibrator should be at a node in
the ultrasonic vibratory motion to avoid damping the ultrasonic
vibration with the mount. It has now been discovered, however, that
with the slotted, bifurcated structure described herein, increased
ultrasonic vibration is obtained by designing the resonant vibrator
with a node shifted from the mount toward the slot. The postulated
theory for this otherwise surprising result is that the ultrasonic
vibration at the bifurcation produces stresses which cause the
bifurcated portions to vibrate transverse to the longitudinal axis
of the resonant vibrator, which transverse vibrations are not
transmitted to the tissue fragmenting end of the resonant vibrator
and thus produce a loss in the vibration transmitted for use. The
stresses producing the transverse vibration are then believed to
decrease more rapidly than the vibration damping losses from
shifting the node away from the mount increase so that net gain in
ultrasonic vibration is achieved by designing the resonant vibrator
with the node shifted from the mount toward the slot.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 of the drawings is a sectional elevation of one version of
the surgical handpiece according to this invention;
FIG. 2 is a sectional elevation of another version of the surgical
handpiece; and
FIG. 3 is a plan of the resonant vibrator employed in the handpiece
of both FIGS. 1 and 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred embodiment is an improved apparatus for
ultrasonically fragmenting and aspirating body tissue. The
apparatus is embodied in a conveniently held handpiece 12, a
cross-sectional view of which is shown in FIG. 1 of drawings,
enclosing means for exciting a resonant member to vibrate in the
ultrasonic range, including an aspirating tool vibrating at its tip
in the ultrasonic frequency range at a longitudinal amplitude in
excess of about 5 mils (0.005 inch).
To achieve such an effect in an instrument which can be
conveniently held by a surgeon, a number of difficult obstacles
must be overcome. One major obstacle is in transmitting excitation
to an operating tool tip while at the same time such tip acts as
the aspirating inlet to effect the surgical removal of the
undesired tissue.
We have discovered that in order to surgically remove a broad
enough range of compliant tissue that the surgeon is apt to
encounter, an instrument which vibrates longitudinally in the range
of at least 5 mils at about 25 KHz is necessary. At the same time
as the tip is ultrasonically vibrating it is desirable to also
apply aspiration to the affected tissue. A number of prior art
issued patents such as previously mentioned do teach the
application of aspiration together with an ultrasonic vibrating
tool tip to remove body tissue. However, it has been found that
except in specific instances where the particular tissue is readily
susceptible to ultrasonic disintegration such as cataracts, it has
been difficult to provide an ultrasonically vibrated tool to
effectively remove tissue exhibiting a wide range of mechanical
properties (i.e., compliance) which the surgeon may encounter in an
operation. Thus, if the ultrasonic instrument was not adaptable to
the range of tissue ordinarily encountered during specific types of
operation, the instrument may have to be discarded for particular
operations and is therefore an inconvenience during the operation.
It is clearly recognized that to be acceptable to the surgeon, an
instrument must be sufficiently rapid and selectively effective
against the various types of tissue the surgeon is desirous of
removing.
In particular, where highly compliant tissue mixed with blood is
aspirated, there is the increased likelihood of occlusion of the
aspiration conduit due to the coagulation of the blood. It is
therefore desirable to provide as large an aspiration path as
possible. This is to avoid clogging or occlusion of the aspiration
path due to the increasing coagulation of the blood tissue mixture
being aspirated. In addition, vibration apparently acts to increase
the rate of coagulation. It is therefore additionally desirable
that the aspiration path or conduit should preferably have minimal
changes of direction of flow and where such changes are required,
they should be as gentle as possible. Further pockets of low flow
velocity are also to be avoided.
Referring to FIG. 1 of the drawings, the surgical instrument 12 is
shown in sectional elevation and comprises a tubular handpiece 14
and an elongated resonant vibrator 16 inserted therein and
projecting out of the front part of the handpiece. As the
instrument is held and manipulated by the surgeon in one of his
hands, the size and weight of the handpiece is limited by the
ability of the hand to delicately grasp and manipulate the
instrument. For this purpose, the outside diameter of the handpiece
should not exceed about 1.5 inches (3.7 cm) in overall diameter and
a diameter of about 1 inch (2.5 cm) is preferred.
Referring now to construction of the resonant vibrator 16, the
vibrator is basically a mechanical vibrating system mounted in the
handpiece. The vibrating system is divided into a transducer; i.e.,
a magnetostrictive stack composed of nickel alloy sandwich such as
is taught in U.S. Pat. No. RE 25,033 and is well known in the art.
Electrical oscillating current supplied to the winding of the coil
induces mechanical oscillations in the stack, such oscillations
being at the resonant frequency and having a maximum practical
peak-to-peak stroke (amplitude) of about 1 thousandth of an inch (1
mil) at a frequency of about 25 KHz. As a practical matter due to
limitations imposed by the state of the art, as frequency increases
in the ultrasonic range, the stroke that one is able to obtain in
the transducer is reduced.
However, it is well known in the art that if one desires to take
the available stroke from the transducer and vary the stroke, an
ultrasonic mechanical transformer may be used. The design of such a
transformer which is fixedly attached to the transducer
magnetostrictive stroke is taught, for instance, in the
aforementioned U.S. Pat. No. RE 25,033.
Finally, the design of the transformer section must include and
yield the preferred characteristics at the output portion of
resonant vibrator. In this regard the output portion of the
vibrator must vibrate ultrasonically with a desired stroke (peak to
peak) of at least 0.005 inch (5 mils) while simultaneously
functioning as an aspirator inlet. The output portion must also,
for surgical requirements, be rather long and slender, while for
aspiration purposes it is preferred to have as large a
cross-sectional flow area as possible to thereby minimize the
possibility of occluding the aspiration conduit.
Prior art hand-held commercial instruments, either providing
irrigation or aspiration through the ultrasonic output end, have
generally had strokes of less than 0.003 inch. Even this level of
stroke is difficult to achieve at 25 KHz in a production
instrument. The resonant vibrator output according to the present
invention is (commercially) capable of producing a stroke in the
range of at least 5 mils and preferably from 5 to 16 mils at about
25,000 cps.
An acceptable ultrasonically vibrated surgical handpiece capable of
such an output; i.e., a stroke of at least 5 mils at 25 KHz, has
not been achieved, whereas we have invented such as described
herein.
FIG. 3 of the drawings illustrates a preferred version of the
resonant vibrator 16 having the magnetostrictive stack 18 at one
end, a tool 20 at the forward end, and a connecting member 22
intermediate the tool 20 and the stack 18. For purposes of
description, the tool encompasses that portion of the vibrator
having an aspiration conduit 24 axially located therethrough. The
tool is also coincidentally a substantially unitary body, designed
for replacement as required and attached to the connecting member
by a male threaded insert 26 at its posterior end. The preferred
tool comprises an elongated hollow tube 28 at its anterior end,
being about 0.09 inch at its tip 30 with a uniform outside diameter
for about 0.65 inch and then tapering uniformly to an outside
diameter of about 0.14 inch over a length of about 2 inches to
fillet 32, where it is machined into a hexagonal neck 34 of about
0.19 inch. The neck 34 is connected to a circular rim 36 of about
0.3 inch diameter and 0.05 inch thickness. From the rim 36, the
previously described male threaded insert 26 which is aout 1/4 inch
long with an O.D. of about 0.21 inch, extends rearwardly and is
chamfered at its end. The threaded insert 26 is necessarily a
relatively large sized thread, being preferably a No. 12 screw
thread, in order to withstand the extreme stresses present. Axially
extending from the rearward end of the insert 26 is a nipple 40
having a neckedin outer surface for receiving and retaining an
aspiration tube 42. The hollow aspiration conduit 24 extends the
whole length of the tool and has a uniform internal diameter (I.D.)
of preferably about 0.06 inch. Preferably the tool is made of a
biologically compatible metal having a low characteristic acoustic
impedance such as titanium or an alloy thereof.
The above-described tool 20, while susceptible to various
modifications, necessarily must have an elongated tubular end
having as small an outside diameter as is practical. Furthermore,
since the tool tip 30 is to vibrate ultrasonically with a stroke in
excess of 0.005 inch (5 mils), the tubular portion of the tool is
tapered over most of its length to preferably reduce the stress to
which the metal is subjected. Finally, and importantly, the tool in
terms of its length and its distributed mass is dynamically a part
of the resonant vibrator 16 which can magnify the 0.001 inch (1
mil) stroke input induced in the magnetostrictive stack 18 to in
excess of a 5 mil output at the tool tip.
The connecting member 22 according to the present invention is a
unitary metal structure also dynamically a part of a resonant
vibrator which serves to connect the stack 18 to the tool 20 and,
more importantly, to serve to transmit and modify the stroke as it
is dynamically transmitted from the stack to the tool. Ideally the
connecting member should be as wide as possible in contrast to the
tool tip, as such a relative diameter increases the magnification,
M, of the output stroke as much as possible at the tool tip in
conformity with the following equation: ##EQU1## where K.sub.1 and
K.sub.2 are constants dependent on the lengths of the various
elements and their material properties and D.sub.1, D.sub.2, and
D.sub.3 are the effective cross-sectional characters of the
connecting member and tool as shown in FIG. 3 of the drawings. It
is therefore readily apparent that the greater the diameter D.sub.1
is in relation to diameters D.sub.2 and D.sub.3, the greater is the
magnification M that is obtained. The node of motion of the
resonant vibrator is located in the vicinity of flange 54, with the
diameter D.sub.1 of the connecting member being on the input side
of the node and the diameters D.sub.2 and D.sub.3 being on the
output side. But, as the portion 46 of the connecting member, which
is defined by D.sub.2 as the effective diameter, comprises the
aspiration path communicating with the hollow tool, it is desirable
to maintain the stroke level in this area as small as possible. If
such connections are made, then the ratio of diameter D.sub.1 to
diameter D.sub.2 should be as small as possible. Such a requirement
modifies the above equation where if D.sub.2 is made much larger
than D.sub.1, M becomes equal to ##EQU2##
Thus the dynamic constraints appear to dictate a large diameter
connecting member in order to achieve high magnification of output
stroke. Since the handpiece 14 in which the vibrator and its
connecting member are mounted has a practical limit to its size, it
being necessary for the surgeon to conveniently hold it in one hand
and manipulate it accurately, it has been previously found
difficult to achieve high magnification in such small
instrumentation.
To achieve such magnification, the connecting member 22 is made of
a metal having a high characteristic acoustic impedance or an alloy
such as monel shaped as shown and described herein. The anterior
portion 46 of the connecting member 22 has a cross-section of about
0.38 inch square and a length of about 1.2 inches where it flares
out to a circular rim 48 with a diameter of about 0.46 inch. The
rim 48 forms the forward edge of an annular cutout 50 of about
0.435 inch diameter, which cutout 50 acts to retain for a first
O-ring 52. The circular flange 54 serves as the rearward boundary
of the cutout and functions to position the vibrator 16 in the
handpiece 14 as will be hereafter described.
The rearward part of the connecting member is a solid circular rod
56 of about 0.28 inch in diameter and about 2 inches long, the
posterior end of which is soldered, brazed, welded or otherwise
fixed to the forward end of the magnetostrictive stack 18.
The anterior portion 46 of the connecting body has an axially
located internally threaded bore 60 being sized to receive the full
length of the male threaded insert 26 of the tool. The bore can
have a shoulder against which the chamfered end of the threaded
insert 26 stops under a predetermined torquing force. A large
rectilinear slot 64 is located in the connecting member adjacent
the end of the borehole and the tool's nipple extends into the
opening formed by the slot. The aspiration tube 42, shown in FIG.
1, is thereby free to mate with the nipple in the opening thus
formed by the slot without the necessity of a sharp radius being
applied at the joint to either the aspiration tube or the
conduit.
Referring again to FIGS. 1 and 2, where the resonant vibrator is
shown mounted in the handpiece, the handpiece has a suitable wound
coil (not shown) for exciting the magnetostrictive stack, and
attached to a cable through which electrical power and signal
conductors and cooling fluid are brought to the handpiece. The
tubular part of the handpiece comprising a housing 80 has an
opening through which the connecting member and stack are inserted.
The housing 66 is undercut and externally threaded at its forward
end. A second O-ring 68 is mounted on the rod 56 and is positioned
between the housing's forward end and the flange 54 upon assembly
of the handpiece.
The two O-rings 52 and 68 thus effectively seal the anterior
portion of the connecting member forward of the flange from the
internal volume of the handpiece enclosing the stack and containing
the various electrical wiring and coolant supply lines in the
handpiece.
A molded retainer 70 is positioned over the connecting member 22
and has an internally threaded cap 72 which is attached to the
housing forward end. Internally forward of its cap, the retainer 70
is molded with a stepped internal diameter to fit over the first
O-ring 52 in compressive contact and over the adjacent flange 54
with some minor clearance. The anterior portion of this stepped
internal diameter is hexagonal in cross-section to enclose the
anterior portion 46 of the connecting member, but with some minor
clearance. Exteriorly the retainer 70 is molded with a dorsally
located opening 74 through its wall adjacent the connecting
member's slot. The opening 74 provides access for surgical grade
plastic tubing 42 to connect to the tool nipple 40. The size of the
opening and the slot is adequate so that the radius of curvature is
gentle, thereby offering less resistance to aspirated blood
containing tissue and lessening the possibility of occlusions
occurring.
FIGS. 1 and 2 also illustrate two versions of an irrigation
manifold 78, each version having a similar hollow truncated cone
surrounding and spaced from the tool to provide an annular
irrigation channel 82 having an annular nozzle 80 about 1/8 inch
posterior to the tip of the tool. The flow of sterile irrigation
fluid through the channel 82 has an effect on the tool output
acting to dampen the vibration somewhat while importantly at the
same time serving to cool the tool over most of its actual
length.
The version of the manifold 78 illustrated in FIG. 1 widens
posteriorly to fit over the retainer 70. The retainer in front of
the opening 72 has a slightly larger outside width end depth, while
the manifold's posterior end is molded with an interior lip 84. The
manifold can therefore in assembly be slid over forward part of the
retainer and when in proper assembled condition is held on the
retainer by the lip 84.
The manifold 90 illlustrated in FIG. 2 has no lip but rather is
tightly fitted over the retainer. The manifold in the second
version has a smaller opening into which an aspiration pip 94 is
inserted into the manifold's dorsal side and opens interiorly
opposite the connecting member slot. The tool, though otherwise
identical to that shown in FIGS. 1 and 2, is shown without its
nipple. Aspirated material therefore flows from the hollow tool
into the space provided by the slot 64 through an opening 70a in
the retainer cap 72a and into the aspiration pipe 94.
An irrigation inlet pipe 88 is inserted fixedly into the cap's
forward part and opened into the annular channel 82. Sterile
surgical tubing (not shown) is connected to the irrigation as
desired from a suitable source. A seal 86, preferably a silastic
washer, is fitted over the anterior part of the connecting member
adjacent a front edge of the retainer and serves to seal the
irrigation fluid space from the space surrounding the connecting
body (and serves as part of the aspiration fluid path in the
handpiece shown in FIG. 2).
Supplying the irrigation fluid through the channel 82 provides
three distinct advantages besides supplying irrigation fluid to the
operative site. The irrigation fluid cools the vibrating tool and
the material, blood, fluid and tissue being aspirated through the
tool. If there is no such provision for cooling the high vibratory
stroke output in excess of 0.005 inch of the tool would rapidly
heat up from such intense vibration and weaken or damage the tool.
Heat would also add to the rate of coagulation of blood being
aspirated through the tool. Reducing the tool temperature thus
reduces the possibility of occlusions. The irrigation fluid also
wets the aspirated tissue, aiding in aspiration thereby. Further,
it protects tissue not in contact with the tip.
The Nodal Position
As is well understood in the design of ultrasonic resonant
vibrators of the general type shown in FIG. 3 for resonant
ultrasonic vibration along the longitudinal axis thereof, the
overall structure is shaped, dimensioned and made of materials
having acoustic properties (as well as other desired properties)
such that the whole has a length which is an integral multiple of
one half the wavelength in its respective parts of the ultrasonic
frequency at which it is resonant. This provides maximum ultrasonic
stroke at the ends and at least one node of no ultrasonic vibration
therebetween at which it is conventional practice, as before
described, to provide a mount 50 for supporting the vibrator
without damping the ultrasonic vibration. In specific example, the
transducer 18 could be, in conventional practice, one half the
resonant wavelength therein long, the portion 22 one quarter
wavelength therein, and the rest to the free end 30 of the tool 20
another quarter wavelength therein so that a node occurrs at the
mount 50.
It has now been discovered, however, that increased ultrasonic
vibration at the tissue contacting end 30 of the tool for the same
input vibrational power can be obtained by redimensioning the
structure shown in FIG. 3, while retaining the otherwise desired
shape as shown in FIG. 3 and the acoustic properties of the
materials (stainless steel which is acoustically similar to monel
being, however, preferably substituted for the before described
monel connecting member 16), so that the node is shifted toward the
slot 64 which bifurcates the connecting member. This is believed to
result from greater gains in damping transverse ultrasonic
vibration into and out of the directions marked by diameter arrows
D.sub.2 in FIG. 3 in the bifurcated portions of the connecting
member along slot 64 than damping losses at the mount 50 from the
elastic O-rings 52, 68.
Specifically, the tool 20 is made of titanium about 3.2 inches from
flange 54 to end 30 with a 0.25 inch hexagonal base, a 0.09 inch
outside diameter end 30, and a 0.07 inch inside diameter aspiration
conduit 24. The connecting member is made of stainless steel with
an overall length of about 2.75 inches an outside diameter of about
0.54 inch in the portion 46, and a hollow portion 22 of an outside
diameter of about 0.33 inch. The slot 64 is about 0.42 inch long
and 0.16 inch wide. The rest of the structure is as before
described, the resonant vibrator then having a somewhat reduced
resonant frequency of about 23 kHz and a node approximately at the
left end of the slot 64 as shown in FIG. 3. The vibration at the
end 30 of the tool, however, is increased. In comparing the 23 kHz
structure just described to the 25 kHz structure before described,
vibrational velocities at the tool end 30 one and one-half times
those of the 25 kHz structure for the same vibratory power are
obtained, a dramatic 50% improvement.
In addition, the maximum stress in the vibrator is also reduced and
distributed more gradually through the structure so that greater
power can be applied without exceeding the strength limits of the
structure. A gauge of this improvement called the Figure of Merit
which is the vibrator gain divided by the maximum stress for the 23
kHz structure over the 25 kHz structure shows a 10% improvement to
about 1.8 from about 1.6.
Although the invention has been described with reference only to
redimensioning the structure shown in FIG. 3 to preserve the
desired aspiration function of the long slot 64 and the
amplification function of the different materials and diameters of
the tool 20 and connecting member 16, it will be appreciated that
changing the shape and acoustic properties of the various
components could also shift the nodal position as described.
Specifically, the tool and connecting member could be combined if
amplification were not desired. These and other variations are
contemplated as within the scope of the claimed invention.
* * * * *